The Python version for a Python app can currently be configured using a runtime.txt file or for Pipenv users via the Pipfile.lock file.

We should support the .python-version file too, since it's more widely used by other tooling in the Python ecosystem.

See also:

• Python Version via .python-version heroku-buildpack-python#932
• Support flexible patch version syntax to allow for automatic Python updates heroku-buildpack-python#913